To isozymes of mouse 3-phosphoglycerate kinase (PGK) were purified to homogeneity by an 8-(6-aminohexyl)-amino-Sepharose column followed by an ion exchange and gel filtration chromatography. Antisera against two PGK isozymes were raised separately in rabbits. Immunological cross-reactivity between the PGK isozymes were investigated by double immunodiffusion and enzyme immuno-inactivation. Amino acid composition and peptide maps were determined for the two PGK isozymes to compare their structural homology.